The present invention relates to a lead frame, a method for manufacturing the same, a resin-encapsulated semiconductor device in which the lead frame and a semiconductor chip are encapsulated with resin, and a method for manufacturing the same. In particular, the present invention relates to a resin-encapsulated semiconductor device manufactured to achieve electrical stability and to improve the high frequency characteristics, a method for manufacturing the same, a lead frame used in the resin-encapsulated semiconductor device, and a method for manufacturing the same.
In recent years, in response to compactness and high density of electronic equipment, there is an demand for high density and high performance of semiconductor components such as resin-encapsulated semiconductor devices, and this trend has promoted the development of more compact and thinner semiconductor components. In this context, a semiconductor device called QFP (Quad Flat Package) in which external terminals are extending outside the encapsulating resin has been improved, and a resin-encapsulated semiconductor device called QFN (Quad Flat Non-leaded Package) or LGA (Land Grid Array) in which lower portions of signal leads that are exposed from a package serves also as an external terminal have been put into practice.
Such a compact and thin resin-encapsulated semiconductor device can be utilized in a communication system employing high frequency. In particular, in mobile communications through cellular phones, PDAs (Personal Digital Assistance) or the like, it is necessary to use a high frequency of 1 GHz or more in order to transmit data with large capacity. For example, in cellular phones, communications in a 1.5 GHz band with WCDMA (wide band CDMA) system will become the main stream in the future. In the resin-encapsulated semiconductor device used in these applications, a semiconductor chip made of a compound semiconductor such as GaAs (gallium arsenic) and SiGeC (silicon germanium carbon) having good high frequency characteristics can be used preferably. In addition, it is necessary to take a measure not to inhibit the characteristics of the semiconductor chip in packaging.
Apart from this, for semiconductor devices, it is generally necessary to stabilize the electrical characteristics by ensuring connection to a ground power. In order to achieve the stability of the electrical characteristics of the resin-encapsulated semiconductor device, in a conventional QFP including a die pad, a semiconductor chip provided on the upper surface of the die pad, suspended leads for supporting the die pad, and signal leads spaced equally apart from each other around the die pad, stable power grounding has been achieved by connecting an electrode pad for grounding on the semiconductor chip and a space portion of the die pad, or the electrode pads and the suspended leads with metal thin wires. Such a structure is also applied to QFN or LGA, as discussed later.
FIG. 46A is a plan view taken from the bottom of a conventional QFN resin-encapsulated semiconductor device. FIG. 46B is a cross-sectional view taken along line XLVIb-XLVIb of the conventional resin-encapsulated semiconductor of FIG. 46A. FIG. 46C is a cross-sectional view taken along line XLVIc-XLVIc of the conventional resin-encapsulated semiconductor of FIG. 46A.
Each of FIGS. 45A and 45B is a view showing an example of a lead frame used in the conventional resin-encapsulated semiconductor device.
As shown in FIGS. 46A to 46C, the conventional QFN resin-encapsulated semiconductor device has a substantially quadrangular bottom surface, and includes a die pad 306, a semiconductor chip 401 mounted on the die pad 306 and having a plurality of electrode pads, a plurality of signal leads 302 that are arranged around the die pad 306 and whose lower surfaces are exposed, metal thin wires 402 connecting the electrode pads of the semiconductor chip 401 and the signal leads 302, suspended leads 305 for supporting the die pad 306, encapsulating resin 403 for encapsulating the upper surface of the signal leads 302, the die pad 306, the metal thin wires 402, and the semiconductor chip 401. In FIG. 46A, the die pad 306 and the suspended leads 305 that are encapsulated are shown by dotted lines. The signal leads 302 are arranged along the four sides of the bottom surface of the device. This type of resin-encapsulated semiconductor device is called “peripheral type”. The suspended leads 305 are exposed in the four corners of the bottom surface of the resin-encapsulated semiconductor device. The suspended leads 305 are connected to the die pad 306 and connected to the electrode pads for grounding of the semiconductor chip 401 by the metal thin wires 402. Thus, the conventional QFN resin-encapsulated semiconductor device is electrically stabilized, as described above.
As shown in FIGS. 45A and 45B, the lead frame used in the conventional QFN resin-encapsulated semiconductor device has the suspended leads 305 having steps 305a that are bent upward, and the upper surface of the die pad 306 is provided in a higher position than the upper surface of the signal leads 302. Thus, a larger semiconductor chip can be mounted on the die pad 306. Furthermore, since the steps 305a are provided, the clamping force applied when resin encapsulation is performed can escape, which prevents the die pad 306 from being dislocated or deformed. Each of the signal leads 302 has a head groove 302b and a base groove 302c, which allows the signal leads 302 to absorb a stress, so that the metal thin wires are hardly broken in the resin-encapsulated semiconductor device. The broken line that surrounds the lead frame in FIGS. 45A and 45B is an outer line 307 of the resin-encapsulated semiconductor device.
Next, FIG. 47A is a perspective view showing an appearance of a conventional LGA resin-encapsulated semiconductor device that is an area array package. FIG. 47B is a cross-sectional view showing the structure of the conventional resin-encapsulated semiconductor device. FIG. 47C is a plan view taken from the bottom surface of the conventional resin-encapsulated semiconductor device.
As shown in FIGS. 47A to 47C, the LGA resin-encapsulated semiconductor device has, for example, a quadrangular bottom surface, and includes a die pad 346, a semiconductor chip 441 mounted on the upper surface of the die pad 346 and having electrode pads, signal leads 342 arranged around the die pad 346, metal thin wires 442 connecting the electrode pads and the signal leads 342, and an encapsulating resin 443 for encapsulating the signal leads 342 on its upper surface side, the die pad 346, the semiconductor chip 441, and the metal thin wires 442. In the bottom surface of the resin-encapsulated semiconductor device, the lower portions of the signal leads 342 are exposed in a circular shape, and they serve as external terminals 344, which are arranged in a matrix. The portion of the die pad 346 excluding the central portion is exposed on the bottom surface of the device. The external terminals that are located in the four corners of the bottom surface among the external terminals 344 are large in size, and used as reinforcement lands serving also as ground terminals 344a. Since the reinforcement lands serving also as ground terminals 344a are connected to the electrode pads for grounding of the semiconductor chip, this resin-encapsulated semiconductor device is electrically stabilized.
Other that those described above, there is SON (Small Outline Non-leaded Package), which has a quadrangular bottom surface in which external terminals are arranged along the opposing sides of the bottom surface, as a resin-encapsulated semiconductor device in which the lower portions of the signal leads function as external terminals. This package is also stabilized electrically in a similar manner.
However, the conventional structures require advanced processing techniques for the lead frame, which is the basic frame of a semiconductor device, in order to reduce the size of the resin-encapsulated semiconductor device and achieve higher density, so that it has been difficult to realize them.
On the other hand, in the structures of the conventional resin-encapsulated semiconductor devices, it is difficult to obtain high frequency characteristics sufficient to be used in high frequency communications or the like. This is mainly because when high frequency signals are input to external terminals adjacent to each other of the resin-encapsulated semiconductor device, the high frequency signals interfere with each other, which causes noise.
For electronic components mounted in a set of equipment such as communication equipment, further higher frequencies are increasingly in demand, and the effects of the noise as described above become large.